The present invention relates to an external reference electrode for use in combination with high temperature, high pressure aqueous systems. Electrodes of this type can be combined with any stable sensing electrodes, such as those used for measuring pH, redox potential and the concentration of specific ions. It is also contemplated that this reference electrode can be used to make in-situ corrosion rate and corrosion potential measurements directly in process system equipment.
Reference electrodes have long been used for determining the characteristics of electrochemical systems. Single electrochemical reactions at electrodes are related by convention to the hydrogen electrode whose potential at all temperatures is taken at zero. Because of the difficulties involved in using the hydrogen electrode as standard in all situations, secondary reference electrodes have been compared with the hydrogen electrode and are widely used. Well known among these are the standard calomel electrodes. For industrial processes requiring in-line applications, other reference electrodes such as Ag/AgCl; Ag/Ag.sub.2 SO.sub.4 or a noble metal such as gold in ferrous/ferric solution as a redox couple are more suitable for use.
Representative reference electrodes are described by Macdonald et al. in "External Reference Electrodes for Use in High Temperature Aqueous Systems", J. ELECTROCHEM. SOC., pp 908-911, June 1979. and by Macdonald in "Reference Electrodes for High Temperature Aqueous Systems - A Review and Assessment", CORROSION, pp. 75-84, NACE 1978. Internal reference electrodes operating at the temperature and pressure of the system can be unstable at temperatures above 150.degree. C. for extended periods of time. Consequently, external electrodes housed in separate compartments maintained at ambient temperature and system pressure have become attractive alternatives. Unfortunately, these electrodes have relatively short lives due to the inevitable contamination of the reference electrode solution by the high pressure system solution. In addition, pressure differentials between electrode solutions and high pressure systems can be difficult and expensive to accurately control.
Therefore, in view of the above discussion, it is an object of the present invention to provide an improved reference electrode assembly.
It is a further object of the invention to provide a long life reference electrode to be used with high temperature and high pressure aqueous systems.
It is a further object of the present invention to substantially eliminate contamination of the reference electrode solution by the system constituents.